1. Field of the Invention
The technic disclosed herein relates to the field of lift control of a thermo-wax for controlling choke valve, fast idle cam and so forth of a carburetor for automobile internal combustion engines.
More particularly, the present invention is concerned with a temperature-responsive control device for carburetors, in which a heat generating body such as a PTC heater, a heat-mass and a thermo-wax are disposed in series in a case from one side of the latter, so that an actuating rod extended from the thermo-wax is projected and retracted in accordance with an expansion and contraction of the thermo-wax thereby to actuate the choke mechanism, fast idle mechanism and so forth of the carburetor.
Still more particularly, in the temperature-responsive control device for carburetors in accordance with the invention, the portion of the heat-mass contactable with the heat-generating body is protruded in an annular form to avoid the surface contact, and the contact of the thermo-wax with the heat-mass is made at the temperature sensing portion of the thermo-wax or, alternatively, by means of a flange in a manner to isolate and float the temperature-sensitive portion.
2. Description of the Prior Art
As is well known, in some carburetors for automobile internal combustion engines, the choke mechanism and the fast idle mechanisms are actuated during warming up of the engine. In the conventional arrangements for actuating such mechanisms, a thermo-wax is heated by a heat-generating body such as PTC element (Positive Temperature Coefficient element) or the like to vary the lift of the actuating rod connected to the thermo-wax, thereby to actuate these mechanisms.
In this type of device, therefore, it is essential that the lift characteristics of the thermo-wax coincides or simulates as much as possible the warming up characteristics of the engine, for otherwise the correct operation of the aforementioned mechanisms will be failed.
Referring to FIG. 1 in which the axis of abscissa represents the time (minute) while axis of ordinate represents the temperature (.theta. .degree.C.), the temperature characteristics P of the PTC heater is such that the Curie point is reached in about 10 seconds after the start-up of the engine, and exhibits a rise much steeper than the cooling water characteristics W which most closely approximates the engine warming up characteristics.
Therefore, if the thermo-wax is heated directly by the PTC heater, the dismissal of the choke valve and the dismissal of the fast idle cam are made at earlier moments than expected during the warming up of the engine, resulting in a deteriorated driveability in the cold state of engine or a re-starting failure due to an over-rich of the mixture.
In order to overcome this problem, it has become a common measure to interpose a heat-mass as a heat-transfer control body between the PTC heater and the thermo-wax, thereby to make the behaviour of the thermo-wax coincide with the state of warming up of the engine.
One of the typical heat masses used heretofore is an area control type heat-mass 1 (type A) as shown in FIG. 2. The area of contact with the PTC heater is reduced by a suitable design of the inside diameter d of the heat mass 1. By so doing, as will be seen from FIG. 4 in which the axes of abscissa and coordinate represent the time T (minute) and the lift L (mm) of thermo-wax, it is possible to delay the increase of the lift. The delay is increased as the diameter d is increased from the small diameter ds to large diameter dl via the medium diameter dm. The lift, however, is decreased to an impractically small level to fail the necessary motion of the choke or other mechanisms, if the diameter d is increased unlimitedly.
FIG. 3 shows a heat-mass 2 of another type (type B). In this case, the increase of the lift is delayed by increasing the volume of the heat-mass from a small volume Ds to a large volume Dl via a medium volume Dm by increasing the outside diameter D as shown in FIG. 5.
In this heat-mass 2, if the diameter D is increased to make the behaviour of the thermo-wax match the engine demand characteristics, the volume of the heat-mass is increased excessively to make is difficult to mount the device on an automobile engine. In addition, the surface area is increased undesirably to cause a reduction in the lift of the thermo-wax.
Therefore, even if well designed, these known heat-mass could provide characteristics far from the cooling water temperature characteristics W shown in FIG. 1, as will be understood from curves A and B in FIG. 1.
Under these circumstances, the present inventors have worked out a heat-input-control type heat mass 3 (type C) on the basis of theory and experiment.
In the heat-mass 3, the portion 4 for opposing and contacting the PTC heater is protruded in an annular form.